Piezoelectric crystal holder



April 1940- R. E. FRANKLIN 7,858

PIEZOELECTRIC CRYSTAL HOLDER Filed July 30, 1938 A wmmwazm INVEN TOR.

' RAL E. FRANKLIN 7fg ww A TTORNEY.

Patented Apr. 23, 1940 PI EZOELECTRIC CRYSTAL HOLDER Ralph Emerson Franklin, Patchogue, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application July so, 1933, Serial "No. 222,080

I 11 Claims.

This invention relates to a new and novel piezoelectric crystal holder having in combination condenser electrodes in which'an air gap between the electrodes is varied by temperature changes.

An object of this invention is to provide a novel compensated crystal holder in which the thermal expansion of two metalscauses a variation in the air gap'between the condenser electrodes to compensate for the temperature coefficient of the crystal. I

Another object of this invention is to provide a crystal holder in which the support elements between the electrodes are arranged to be varied according to a desired degree of temperature compenation.

Briefly, this invention relates to the use of a bimetallic thermostat metal in a crystal holder where crystals of other than zero temperature frequency characteristics are used. The recent trend in the use of piezoelectric crystal oscillators for the control of radio frequency transmitters is toward crystals of zero frequency temperature characteristics. However, it has been found that the cost of producing such crystals is very expensive and a large percentage of these crystals have a small frequency temperature characteristic either plus or minus. I I

The purpose of this invention is to use crystals with small or medium frequency temperature characteristics in a holder which has means for compensating to give a constant frequency over a wide range of temperature variation. The principle upon which this invention operates can best be understood by referring to the accom panyingdrawing, inywhich: I

Fig. 1 is a plan view ofthe crystal holder;

Fig. 2 is a cross-sectional view of Fig. 1, taken on lines 2-2 of Fig. 1;

Fig. 3 is a. plan view showing in detail one method of supporting the bimetallic strip elements; I

Fig. 4 is an end elevation partly in section of Fig. 3;,

Fig. 5 is a plan view of another method of holding the bimetallic strips; and

Fig. 6 is a sectional view partly in section of Fig. 5.

Referring now in detail to the'drawing, I is the lower electrode which is made of any low resistant conductive material, such as brass or Monel metal, silver plated. Lower electrode I is preferably mounted upon any suitable support 2 by two insulating posts 3 by means of screws 4. The piezoelectric crystal plate 5 is positioned on lower electrode I by any suitable means, such as retaining fingers 6, but free to move slightly. An upper electrode 1, which ispreferably made of brass or Monel metal with a silver lower surface 8 is supported from an external ring 9 by means of three bimetallic strips III, the ring 9 being secured to lower electrode I and insulated from it by means of three screws II, insulators I2,

springs I3 and insulating spacers I4. The bii metallic strips I are adjustably arranged upon ring 9 by means of three clamp members I and three screws I6, shown in detail in Figs. 3 and 4, or if desired, the bimetallic strips may be slotted by means of a slot I1, shown'in Figs. 5 and 6, through which a clamp screw I8 passes, the suspension of the upper electrode being such that an air gap I9 acts as avariable dielectric or capacitive space between electrodes I and I, which amount of gap varies upon a change of temperature. Thev amount of compensation is determined by the length of the bimetallic strip. Electrical connection can be madeto electrode 1 by means of a stud and nut 22, the connection to the lower electrode being made by any suitable means such as a metallic strip 23, placed between insulating posts 3 and clamped by means of screws 4. The operation of this improved holder is as follows:

.Given a crystal of small or medium positive frequency temperature characteristic, as the temperature of the holder rises due to heat from the crystal or other source, the frequency would rise if the air gap I9 remained constant. In this invention, the upper electrode being suspended by bimetallic strips of such length that the air gap is changed by such a value so as to compensate for a Change in frequency, the bimetallic strips are placed so thatthe air gap is reduced to compensate for a rise in temperature characteristic. If the crystal should have a negative characteristic, the bimetallic strips can be turned over to give an increased air gap with rising temperature. This invention should not be limited to the precise modification shown as it is well known to those skilled in the art that it is capable of taking other forms and shapes.

What is claimed is:

1. A piezoelectric crystal holder comprising a lower fixed electrode, a variable electrode located above said fixed electrode, a piezoelectric crystal interposed between said electrodes, an air gap between one of,sa.id electrodes and said crystal, and means for varying the air gap with variations in temperature, said means comprising an annular member surrounding said variable electrode, a plurality of bimetallic strips secured to said variable electrode and supported from said annular member, and a plurality of binding members for securing said annular member to said fixed electrode.

2. A piezoelectric crystal holder comprising a lower fixed electrode, a variable electrode located above said fixed electrode, a piezoelectric crystal interposed between said electrodes, an air gap between one of said electrodes and said crystal, means for varying the air gap with variations in temperature, said means comprising a plurality of bimetallic strips insulatingly supported from at least one of said electrodes, and means for adjusting the len th of said bimetallic strips.

3. A piezoelectric crystal holder comprising a lower fixed electrode, a variable electrode located above said fixed electrode, a piezoelectric crystal interposed between said electrodes, an air gap between one of said electrodes and said crystal, means for varying the air gap with variations in temperature, said means comprising a plurality of bimetallic strips insulatingly supported from at least one of said electrodes, and means for adjusting the length of said bimetallic strips by a plurality of upright support members having slots to slide said bimetallic strips to vary their length.

4. A piezoelectric crystal holder comprising a lower fixed electrode, a variable electrode located above said fixed electrode, a piezoelectric crystal interposed between said electrodes, an air gap between one of said electrodes and said crystal, means for varying the air gap with variations in temperature, said means comprising a plurality of bimetallic strips insulatingly supported from at,least one of said electrodes, and means for adjusting the length of said bimetallic strips by a plurality of upright support members, said bimetallic strips having a slot to vary the length thereof.,

5. A piezoelectric crystal holder comprising a fixed and a variable electrode, a piezoelectric crystal interposed between said electrodes, a ring supported above said fixed electrode and surrounding said variable electrode, insulating members for supporting said ring, an air gap between one of said electrodes and said crystal, and means coupled between said variable electrode and said ring for varying the air gap with variations in temperature.

6. A piezoelectric crystal holder comprising a lower fixed electrode, a variable electrode located above said fixed electrode, a piezoelectric crystal interposed between said electrodes, an air gap between one of said electrodes, and said crystal, and means for varying the air gap with variations in temperature, said means comprising an annular member surrounding said variable electrode, three bi-metallic strips secured to said variable electrode and supported by said annular member, and three insulating spacing members mounted on said fixed electrode to secure said an-- nular member thereto.

7. The combination of a piezoelectric crystal and a variable electric condenser comprising fixed and variable condenser electrodes, a piezoelectric crystal interposed between said electrodes, an air gap between one of said electrodes and said crystal, and means for varying the capacity between said electrodes upon variations in temperature of said crystal by varying said air gap, said means comprising an annularmember surrounding said variable condenser electrode, a plurality of bimetallic strips secured to said variable condenser electrode and said annular member, said annu ar member insulatingly supported from said fixed electrode by binding means.

8. A piezoelectric crystal holder having temperature compensation means comprising a lower fixed electrode, a variable electrode located above said fixed electrode, a piezoelectric crystal interposed between said electrodes, an air gap between one of said electrodes and said crystal, means for varying the air gap with variations in temperature, said means comprising a plurality of bimetallic strips insulatingly supported from at least one of said electrodes, and means for adjusting the length of said bimetallic strips by a plurality of clamp members for securing said bi-metallic strips to said fixed electrode to vary the amount of temperature compensation of said holder.

9. A piezoelectric crystal holder having temperature compensation means comprising a lower fixed electrode, a variable electrode located above said fixed electrode, a piezoelectric crystal interposed between said electrodes, an air gap between one of said electrodes and said crystal, means for varying the air gap with variations in temperature, said means comprising a plurality of bi-metallic strips supported from at least one of said electrodes, and means comprising a clamping member arranged to slide in a slot in said b1- metallic strips to vary the length thereof to alter the amount of temperature compensation of said holder.

10. A piezoelectric crystal holder comprising a iower fixed electrode, a variable electrode located above said fixed electrode, a piezoelectric crystal interposed between said electrodes, an air gap between one of said electrodes and said crystal, means for varying the air gap with variations in temperature, said means comprising a plurality of bimetallic strips insulatingly supported from at least one of said electrodes, means for adjusting the length of said bimetallic strips, and a terminal member located on said variable electrode andsaid fixed electrode to make electrical connection thereto.

11. A piezoelectric crystal holder comprising a lower fixed electrode, a variable electrode located above said fixed electrode, a piezoelectric crystal interposed between said electrodes, an air gap between one of said electrodes and said crystal, and means for varying the air gap with variations in temperature, said means comprising an annular member surrounding said variable electrode, a plurality of bimetallic strips secured to said variable electrode and supported from said annular member, a plurality of insulating spacers and a plurality of binding members having spring tension means, said binding members passing through an aperture in said annular member and said spacers to insulatingly secure said annular member to said fixed electrode.

RALPH EMERSON FRANKLIN. 

